A new diagnostic rule for deep vein thrombosis: safety and efficiency in clinically relevant subgroups

Background. Recently, a new, simple diagnostic rule was introduced to enable GPs to safely refrain from referring a considerable proportion of the patients suspected of having deep vein thrombosis (DVT). The rule (which includes seven patient history and physical examination items plus the result of a D-dimer test) discriminates 'very low' risk patients (not to be referred) from patients with an increased risk of DVT (to be referred). However, the rule's 'efficiency' (proportion of patients designated by the rule as very low risk) and safety (DVT prevalence among these very low risk patients) may change according to patient characteristics. Objective. To test the rule's safety and efficiency in clinically relevant subgroups; i.e. across three age groups, in men and women, and in patients with and without a history of DVT, separately. Methods. We retrospectively analysed data of 2086 primary care patients suspected of DVT, in whom all rule items and the result of the reference ('gold') standard (compression ultrasonography) were collected. Results. The rule's efficiency decreased with age from 38.1% in the relatively young (< 50 years) compared to 9.8% in patients aged >= 70 years. The percentage of DVT among the very low risk patients was < 1.5% in all subgroups. The low efficiency in the elderly could be improved without compromising the safety by increasing the D-dimer threshold. Conclusion. The rule can safely exclude DVT in primary care patients suspected of DVT, irrespective of age, gender and history of DVT.